Combined Ion Beam And Molecular Beam Epitaxy Research Articles

Low-energy nitrogen-ion doping into GaAs and its optical properties

Abstract Nitrogen (N) ions were impinged during the epitaxial growth of GaAs using combined ion beam and molecular beam epitaxy (CIBMBE) method. Low-temperature photoluminescence measurements showed that incorporated nitrogen ([N] 18 cm −3 ) is optically active with a substrate temperature of 550°C and a N + ion acceleration energy of 100 eV. For higher [N] of ∼2×10 18 cm −3 , N-related emissions can be found after high temperature (650–850°C) annealing. We discuss the annealing effects and also the novel emissions found after annealing at high temperature (750°C) with a [N] of ∼1×10 19 cm −3 .

Carbon Doping into GaAs Using Low-Energy Hydrocarbon Ions

AbstractThe role of hydrogen (H) in carbon (C)-doped GaAs was examined by co-doping of C and H atoms using low-energy hydrocarbon (CH+ and CH3+) ions. Experiments were carried out using the combined ion beam and molecular beam epitaxy (CIBMBE) system. Samples were characterized by low-temperature photoluminescence at 2K and Hall effect measurements at room temperature. Results show that incorporated C atoms are optically and electrically activated as acceptors even by hydrocarbon ion impingement. The effect of H incorporation was found to be noticeable when impinged current density of CH3+ ion beam is high that produces equivalent net hole carrier concentration greater than ∼1018 cm−3

Optical characterization of low-energy nitrogen-ion doped GaAs

Optical characterization of nitrogen (N)-doped GaAs was performed by low-temperature photoluminescence (PL) measurements. N doping in GaAs was successfully made by irradiating low-energy (100 eV) N + ion beam during the growth of GaAs using the combined ion beam and molecular beam epitaxy (CIBMBE) system. For the sample with N + ion beam current density ( I N) of 3 nA/cm 2, which correspond to N concentration ([N]) of ∼5 × 10 17 cm −3, two sharp PL emissions were observed at 1.508 eV ( X 1) and 1.495 eV ( X 2). For the sample with I N of 75 nA/cm 2 ([N] ≈ 1 × 10 19 cm −3), several novel PL emissions tentatively labeled by Y j ( j = 1, …, 8) were observed in the energy range of 1.491 – 1.449 eV by furnace annealing at 750°C for 20 min. Photoluminescence excitation measurements indicated that X 1 is correlated with the PL emission at 1.514 eV. Since the energy separation between individual Y j ( j = 1, …, 8) and X 2 is almost linear to r k −3, where r k is the distance between nitrogen-nitrogen (NN) pairs, we ascribed X 2 and Y j as the radiative transition of excitons bound to isolated N and that to NN pairs, respectively.

Low energy nitrogen ion doping into GaAs using combined ion-beam and molecular-beam epitaxy method

Low energy nitrogen (N) ions were irradiated during the epitaxial growth of GaAs using combined ion beam and molecular beam epitaxy (CIBMBE) method as a function of N + ion acceleration energy ( E a) and N + ion beam current density ( I N). E a was varied from 70 to 170 eV I N from 900 pA/cm 2 to 75 nA/cm 2. GaAs growth rate was fixed to 1 μm/h. In 2 K photoluminescence (PL) spectra of the samples with I N = 3 nA/cm 2 and E a = 70–100 eV, two sharp emissions at 1.508 eV ( X 1) and 1.495 eV ( X 2), which have been attributed to the emissions of excitons bound to isolated N atoms, and another one at 1.443 eV ( X 5) were observed. These results show that nitrogen (N) atom in GaAs becomes optically active as an isoelectronic impurity at least in as-grown condition. For N + ion-irradiated samples with rather high I N, e.g., with I N = 75 nA/cm 2 and E a = 100 eV, a broad emission together with multiple sharp ones were observed after furnace annealing at 750°C which were ascribed to emissions of excitons bound to nitrogen-nitrogen (NN) pairs.

Growth of Ge1−xCx, Alloys on Si by Combined Low-Energy Ion Beam and Molecular Beam Epitaxy Method

AbstractA combined ion beam and molecular beam epitaxy (CIBMBE) method was applied for the deposition of a Ge1−x, Cx, alloy on Si(100) using a low-energy ( 50 – 100 eV ) C+ ion beam and a Ge molecular beam. Metastable Ge1−xCx solid solutions were formed up to x= 0.047, and the CIBMBE method was shown to have a very high potential to grow metastable Ge1−xCx alloys. It was also revealed that the sticking coefficient of C+ ions into Ge was ˜28% for Ei = 100 eV and ˜18% for Ei. = 50 eV. Structural characterization suggests that the deposited films are single crystals grown epitaxially on the substrate with twins on {111} planes. Characterization of lattice dynamics using Raman spectroscopy suggested that the deposited layers have a small amount of ion irradiation damage.

Growth of Ge1-xCx Alloys on Si by Combined Low-Energy Ion Beam and Molecular Beam Epitaxy Method

AbstractA combined ion beam and molecular beam epitaxy (CIBMBE) method was applied for the deposition of a Ge1-xCx alloy on Si(100) using a low-energy ( 50 – 100 eV ) C+ ion beam and a Ge molecular beam. Metastable Ge1-xCx solid solutions were formed up to x = 0.047, and the CIBMBE method was shown to have a very high potential to grow metastable Ge1-x,Cx alloys. It was also revealed that the sticking coefficient of C+ ions into Ge was ∼28% for Ei, = 100 eV and ∼18% for Ei = 50 eV. Structural characterization suggests that the deposited films are single crystals grown epitaxially on the substrate with twins on {111} planes. Characterization of lattice dynamics using Raman spectroscopy suggested that the deposited layers have a small amount of ion irradiation damage.

Heavily carbon-doped GaAs layers prepared by low-energy ion-beam impingement during molecular beam epitaxy

Low-energy (170 eV) C + ion-beam doping during molecular beam epitaxy of GaAs was carried out using a combined ion beam and molecular beam epitaxy (CIBMBE) system. Incorporated C atoms were both electrically and optically well-activated as acceptors with doping levels up to 4 × 10 19 cm −3 in the as-grown condition. In low temperature (2 K) photoluminescence (PL) spectra, C-related specific emissions were clearly observed, indicating good quality of the films. To understand the advantages of low-energy process by CIBMBE, film quality and the rate of C activation were compared with those obtained from 400 keV hot implantation of C at substrate temperatures up to 600°C. Through Raman scattering, 2 K PL and Hall effect measurements, it was found that the use of a low-energy C + ion beam offers advantages such as low damage doping and good activation rate of incorporated C atoms.

Carbon doping into GaAs using combined ion beam and molecular beam epitaxy method

Carbon (C) doping by combined ion beam and molecular beam epitaxy (CIBMBE) was investigated. In this technique, mass-analyzed C ions (12C+) are accelerated at low energies of 30 to 1000 eV and are irradiated onto growing GaAs substrate. Doping concentration control in CIBMBE can be very stably accomplished by simply adjusting the ion beam current density, which is independent of growth conditions of host materials. Experiments on systematic variation of C+ ion acceleration energy (EC+) indicated that, in the energy range of EC+ <170 eV, net hole concentration (|NA − ND|) increases slightly as EC+ increases. The highest |NA − ND| is obtained at EC+ = 170 eV under the constant C+ ion beam current density. For EC+ > 170 eV, |NA − ND| decreases dramatically with increasing EC+, which can be explained in terms of enhanced sputtering effect. Although no evidence of damages induced by ion irradiation is shown for low EC+ range of ≤170 eV, trace of damages is apparently observed for EC+ > 170 eV.

Carbon doping into GaAs using combined ion beam and molecular beam epitaxy method

Carbon (C) doping by combined ion beam and molecular beam epitaxy (CIBMBE) was investigated. In this technique, mass-analyzed C ions ( 12C +) are accelerated at low energies of 30 to 1000 eV and are irradiated onto growing GaAs substrate. Doping concentration control in CIBMBE can be very stably accomplished by simply adjusting the ion beam current density, which is independent of growth conditions of host materials. Experiments on systematic variation of C + ion acceleration energy ( E C + ) indicated that, in the energy range of E C + <170 eV, net hole concentration (| N A − N D |) increases slightly as E C + increases. The highest | N A − N D | is obtained at E C + = 170 eV under the constant C + ion beam current density. For E C + > 170 eV, | N A − N D | decreases dramatically with increasing E C + , which can be explained in terms of enhanced sputtering effect. Although no evidence of damages induced by ion irradiation is shown for low E C + range of ≤170 eV, trace of damages is apparently observed for E C + > 170 eV.

Hyperthermal (30–500 eV) C + ion-beam doping into GaAs during molecular beam epitaxy

Ion-beam doping of GaAs with hyperthermal (30–500 eV) carbon ion (C +) has been investigated using a combined ion beam and molecular beam epitaxy (CIBMBE) system. The CIBME system is a combination technique between a low-energy ion accelerator and a solid-source MBE, which are connected under ultra-high vacuum (UHV) condition. C +-doping was carried out during GaAs MBE growth at substrate temperature of 550°C with the same C + beam current density. Grown layers were characterized by low-temperature (2 K) photoluminescence and room temperature Hall effect measurements, and it was revealed that the incorporation behavior of C significantly depends on the acceleration energy of C + ( E C). The highest net hole concentration (∥ N A − N D∥) was obtained at E C + = 170 eV. In the energy range of E C + < 170 eV, ∥ N A − N D∥ slightly increased as E C + increased, and for E C + > 170 eV ∥ N A − N D∥ dramatically decreased with increasing E C + , which can be explained in terms of enhanced sputtering effect. On the other hand, ion-beam induced radiation damages were observed for E C + > 170 eV.

Fabrication of Epitaxial Silicides thin films by Combining Low-Energy Ion Beam Deposition and Silicon Molecular Beam Epitaxy

AbstractWe have developed successfully the combined ion beam and molecular beam epitaxy (CIBMBE) system with a newly designed Knudsen cell for Si effusion. The CIBMBE system was applied to the epitaxial growth of Sil., Cx alloy thin films on Si using low-energy ( 100 – 300 eV ) C+ ion beam. Preliminary results on the characterization of the deposited films suggest high potential and reliability of the new Knudsen cell for Si effusion, as well as high ability of the CIBMBE method to produce thermally non-equilibrium materials. In addition, they indicate that the value of x decreases with increasing IC, which suggests that the selective sputtering for deposited C atoms by incident C+ ion beams takes place during CIBMBE processing. Precipitates of β-SiC were also found to be formed in the deposited films, whose amount was observed to increase with increasing IC.

Ion-beam doping of GaAs with low-energy (100 eV) C+ using combined ion-beam and molecular-beam epitaxy

A combined ion-beam and molecular-beam-epitaxy (CIBMBE) system has been developed. This system consists of an ion implanter capable of producing ions in the energy range of 30 eV–30 keV and conventional solid-source MBE. As a successful application of CIBMBE, low-energy (100 eV) carbon ion (C+) irradiation during MBE growth of GaAs was carried out at substrate temperatures Tg between 500 and 590 °C. C+-doped layers were characterized by low-temperature (2 K) photoluminescence (PL), Raman scattering, and van der Pauw measurements. PL spectra of undoped GaAs grown by CIBMBE revealed that unintentional impurity incorporation into the epilayer is extremely small and precise doping effects are observable. CAs acceptor-related emissions such as ‘‘g,’’ [g-g], and [g-g]β are observed and their spectra are significantly changed with increasing C+ beam current density Ic. PL measurements showed that C atoms were efficiently incorporated during MBE growth by CIBMBE and were optically well activated as an acceptor in the as-grown condition even for Tg as low as 500 °C. Raman measurement showed negligible lattice damage of the epilayer bombarded with 100 eV C+ with no subsequent heat treatment. These results indicate that contamination- and damage-free impurity doping without postgrowth annealing can be achieved by the CIBMBE method.

Effects of Carbon-Ion Irradiation-Energies on the Molecular Beam Epitaxy of GaAs and Ingaas

AbstractCarbon ion (C+) irradiation during molecular beam epitaxy (MBE) growth of GaAs/GaAs and in0.53.Ga0.47As/InP layers was carried out using CIBMBE (combined ion beam and molecular beam epitaxy) method as a function of wide acceleration energy (Ea=30 eV-30 keV) at a constant ion beam current density. Judging from the monitored current density and the net hole concentration (INA-ND|) obtained from Hall effect measurements, activation rate as high as 88% was achieved for as-grown GaAs layers by C+ ion irradiation of Ea=~170eV. It was revealed that by annealing at 800°C, a slight enhancement (~ 10%) of INA-ND| is practiced for Ea &lt;~ 130eV but a significant increase of INA-ND| is realized for Ea&gt;~lkeV. IN in0.53Ga0.47As/InP layers with increasing Ea, a type conversion of electric conduction from n to p was found to occur at Ea= ~70~100eV. these observations describe that Ea plays a vital role to determine the location of incorporated electrical and optical active impurities in GaAs and inGaAs. Further for comparison, C+-implanted GaAs layers were prepared by high-energy (400 keV) ion-implantation as a function of substrate temperature (T1=RT-600 °C). For C dose concentration of lxl018cm-3\ the highest activation rate of ~20 % was obtained at T1=~150 °C. This result states that CIBMBE method is a superior doping method in view of activation rate of introduced dopants and the formation of damage-free ion-irradiated layers.

Low energy (100 eV) C+ ion doping into GaAs using combined ion beam and molecular beam epitaxial technology

Low-energy (100 eV) carbon ion (C+) irradiation during molecular beam epitaxy of GaAs was carried out using combined ion beam and molecular beam epitaxy (CIBMBE) technology for the growth temperature (Tg) range between 500 and 590 °C. Carbon incorporation was identified by both low-temperature (2 K) photoluminescence and Hall effect measurements. In the PL spectra, two well-established specific emissions, ‘‘g’’ and [g-g], which are closely related to acceptor impurities, were observed for the above Tg range. The results indicate that carbon was both optically and electrically well activated as an acceptor even at Tg as low as 500 °C. Maximum net hole concentration, ‖NA-ND‖, as high as 3×1018 cm−3 was obtained with no appreciable radiation damages and undesired impurity contamination.

Damage-Free Ion Beam Doping of Carbon During Molecular Beam Epitaxy of GaAs

ABSTRACTRecently, we introduced various acceptor impurities into MBE-grown ultra-pure GaAs by conventional high-energy ion implantation and found many novel shallow emissions associated with acceptor-acceptor pairs. Most of these emissions were easily quenched by extremely small amount of residual donor atoms which were unintentionally introduced during doping processes. For the interpretation of impurity effects, the usage of mass-separated atom as dopant source was strongly suggested. Along this consideration, we developed combined ion beam and molecular beam epitaxy (CIBMBE) technology, in which damage-free doping with high mass purity (M/ΔM=100) is expected to be possible. We here present the results of low-energy (100 eV) carbon ion doping using CIBMBE method. Samples were prepared asa function of growth temperature (Tg=400-700°C) and ion beam current. Net hole concentration, |NA-ND| as high as ~1×1020 cm-3 was obtained in as-grown samples. In 2K photoluminescence spectra, emissions due to acceptor-acceptor pairs exhibit specific energy shift with growing |NA-ND|. Results indicate that carbon doping can be made efficiently even at Tg as low as 500°C without any post heat treatment. These results also tell that by CIBMBE method no serious radiation damages are produced and the undesired impurity contamination can be considerably suppressed.

Optical Characterization of 100 eV C+ Ion Doped GaAs

ABSTRACTLow energy (100 eV) impinging of carbon (C+) ions was made during molecular beam epitaxy (MBE) of GaAs using combined ion beam and molecular beam epitaxy (CIBMBE) technologies for the growth temperature ( Tg ) between 500 °C and 590 °C. 2 K photoluminescence (PL), Raman scattering and Hall effect measurements were made for the samples. In the PL spectra two specific emissions, “g” and [g-g], were observed which are closely associated with acceptor impurities. PL and Hall effect measurements indicate that C atoms were very efficiently introduced during MBE growth by CIBMBE and were both optically and electrically well activated as acceptors even at Tg=500 °C. The results reveal that defect-free impurity doping without subsequent annealing can be achieved by CIBMBE method.